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United States Patent |
6,082,174
|
Lee
,   et al.
|
July 4, 2000
|
Apparatus and method for determining the amount of entrapped gas in a
material
Abstract
An entrapped gas measuring apparatus includes a reservoir housing with a
reservoir which is adapted to receive a material sample and to expand
according to an expansion of the material sample when a negative pressure
is applied externally to the reservoir. A parameter indicating the change
in volume of the reservoir during the expansion, such as the actual change
of volume of the reservoir or a change in position of a moveable wall
which at least in part defines the reservoir, is detected by a detector. A
processor coupled to the detector is used to determine the amount of
entrapped gas based upon the detected parameter. The amount of entrapped
gas determined by the processor may be the percent volume of the entrapped
gas in relation to the overall volume of the sample, or may be the actual
volume of the entrapped gas in the sample. Based at least in-part upon the
measured amount of entrapped gas within the sample, the processor is
further adapted to determine at least one of: percent volume of the
substrate in the sample in relation to the overall volume of the sample;
actual volume of the substrate in the sample; or density of the sample or
substrate within the sample. The entrapped gas measuring apparatus may be
used to produce a material having a known amount of entrapped gas by:
making a first material according to a first method and which has a first
amount of entrapped gas; applying a negative pressure to the sample such
that the sample expands from a first volume to a second volume; detecting
a parameter which is indicative of the change of sample volume under the
applied negative pressure; comparing the detected parameter with a
predetermined range for the parameter; and, if the detected parameter is
not within the predetermined range, making a second material according to
a second method which has a second amount of entrapped gas that is within
the predetermined range.
Inventors:
|
Lee; Charles E. (Union City, CA);
Della-Santina; John D. (Novato, CA)
|
Assignee:
|
Benchtop Machine and Instrument, Inc. (Fairfax, CA)
|
Appl. No.:
|
132630 |
Filed:
|
August 11, 1998 |
Current U.S. Class: |
73/19.08; 73/60.11 |
Intern'l Class: |
G01N 033/38; G01N 037/00 |
Field of Search: |
73/60.11,19.08,19.05,19.01,19.09,19.1
|
References Cited
U.S. Patent Documents
2138141 | Nov., 1938 | Cromer et al. | 73/19.
|
2280086 | Apr., 1942 | Hayward | 324/693.
|
2749220 | Jun., 1956 | Rochon | 436/32.
|
3521478 | Jul., 1970 | Magorien | 73/19.
|
3731530 | May., 1973 | Tanguy et al. | 73/152.
|
3766786 | Oct., 1973 | Gebatia et al.
| |
4072046 | Feb., 1978 | Lao.
| |
4083228 | Apr., 1978 | Turner et al.
| |
4095473 | Jun., 1978 | Batchelor et al.
| |
4184371 | Jan., 1980 | Brachet.
| |
4329869 | May., 1982 | Toda | 73/19.
|
4369652 | Jan., 1983 | Gundlach.
| |
4416154 | Nov., 1983 | Schaffer et al.
| |
4573342 | Mar., 1986 | Jones.
| |
4640130 | Feb., 1987 | Sheng et al.
| |
4700561 | Oct., 1987 | Dougherty | 73/19.
|
4837776 | Jun., 1989 | Poll | 374/56.
|
4852395 | Aug., 1989 | Kolpak | 73/61.
|
4969356 | Nov., 1990 | Hartstein.
| |
5022261 | Jun., 1991 | Wolfson et al.
| |
5074146 | Dec., 1991 | Orr et al.
| |
5133219 | Jul., 1992 | Camp.
| |
5535624 | Jul., 1996 | Lehmann.
| |
5576499 | Nov., 1996 | Davies.
| |
Other References
Product brochure for Volumetair; Press-Ur-Meter; and Roll-A-Meter, A Simple
Device for Measuring Entrained Air, Gilson Company, Inc., 8 pages, Aug.
1997.
Standard Test Method for Air Content of Freshly Mixed Concrete by the
Pressure Method, ASTM Designation C231-91b, pp. 130-137, Jan. 1992.
Standard Test Method for Open-Cell Content of Rigid Cellular Plastics by
the Air Pycnometer, ASTM Designation D 2856-94, pp. 143-147.
|
Primary Examiner: Williams; Hezron
Assistant Examiner: Politzer; Jay L.
Attorney, Agent or Firm: Peacock III; James C., O'Banion; John P.
Claims
What is claimed is:
1. An assembly for measuring an amount of entrapped gas in a material
sample in a test environment, comprising:
(a) a reservoir configured to receive the material sample, said reservoir
having first and second sections, said second section being adjustable in
position relative to the first section from a first position to a second
position such that the reservoir has an adjustable volume from a first
volume to a second volume, respectively, when the material sample is
received within the reservoir and a predetermined pressure which is
negative relative to atmospheric pressure in the test environment is
applied to the reservoir, the position of the second section relative to
the first section being indicative of the volume of the reservoir;
(b) a detector coupled to said second section and configured to measure the
position of the second section relative to the first section;
(c) a processor which is coupled to the detector and which is configured to
determine an amount of entrapped gas within the material sample received
within the reservoir based upon a change in the position of the second
section from the first position to the second position; and
(d) a vacuum chamber enclosing said reservoir and configured to apply said
negative pressure to said reservoir;
(e) wherein said material sample expands in response to application of said
negative pressure to said reservoir,
(f) wherein the first volume of the reservoir is substantially equal to the
volume of the material sample at atmospheric pressure in the test
environment,
(g) wherein the second volume of the reservoir is substantially equal to
the volume of the material sample when the material sample expands after
applying the negative pressure to the reservoir, and
(h) wherein the differential between said second volume of said reservoir
and said first volume of said reservoir is indicative of the amount of gas
entrapped in said material sample.
2. The assembly of claim 1, wherein
the reservoir is further defined by a reservoir chamber which is relatively
rigid,
the wall has a zero position relative to the reservoir chamber which is
characterized by the reservoir's volume being substantially equal to zero
prior to receiving the material sample within the reservoir, and
the processor determines the amount of entrapped gas at atmospheric
pressure in the test environment by the equation: (d.sub.2
-d.sub.1)/(d.sub.1 -d.sub.0)*100, such that d.sub.0 is the zero position,
d.sub.1 is the first position, d.sub.2 is the second position, P.sub.a is
the atmospheric pressure in the test environment, and P.sub.v is the
negative pressure applied to the reservoir.
3. The assembly of claim 2, wherein the housing further comprises:
a syringe with a barrel and a plunger, the barrel having a front end and a
rearward end and also an inner surface which forms an inner bore with a
longitudinal axis that extends between the front and rearward ends, and
the plunger having a front end and a rearward end; and
a front wall which is engaged to and is adapted to form a gas tight seal
with the front end of the barrel,
wherein the front end of the plunger is engaged within the barrel's inner
bore through the rearward end of the barrel and includes the wall as a
rearward wall which is slideably coupled to the barrel's inner surface
with a gas tight seal between the inner bore and the rearward end of the
barrel,
wherein the reservoir is defined by the front wall, the barrel's inner
surface, and the rearward wall, and
wherein the first and second positions of the wall are along the
longitudinal axis of the inner bore.
4. The assembly of claim 1, wherein the processor is adapted to determine
the amount of entrapped gas as a percent volume of the material sample
which represents an actual volume of entrapped gas within the material
sample divided by the volume of the material sample.
5. The assembly of claim 4, wherein the processor is adapted to determine
the actual volume of entrapped gas within the material sample by
multiplying the percent volume of entrapped gas by the volume of the
material sample.
6. The assembly of claim 5, wherein the material sample further comprises a
substrate, and the processor is adapted to determine a volume of the
substrate by subtracting entrapped gas volume from the overall material
sample volume.
7. The assembly of claim 6, wherein the processor is further adapted to
determine a density of the substrate by dividing the substrate mass by the
substrate volume.
8. The assembly of claim 1, wherein the sample is selected from the group
consisting of semi-solids, finely divided solids, and liquids.
9. The assembly of claim 1, further comprising a vacuum source in fluid
communication with said vacuum chamber, wherein said vacuum chamber
sealably encapsulates said reservoir, and wherein said vacuum source
applies a negative pressure within the vacuum chamber to effect a
reduction in pressure surrounding said reservoir and a corresponding
expansion of said reservoir as a result of expansion of the sample under
reduced pressure.
10. A method for measuring an amount of entrapped gas within a material
sample in a test environment, said material sample having a volume which
is adjustable under an applied negative pressure, comprising the steps of:
(a) placing the material sample in an expandable reservoir;
(b) placing said reservoir in a vacuum chamber;
(c) applying negative pressure to the reservoir, said negative pressure
being negative relative to atmospheric pressure in the test environment
such that the reservoir expands from a first volume to a second volume as
a result of expansion of said material sample;
(d) detecting the expansion in volume of said reservoir from the first
volume to the second volume; and
(e) determining an amount of entrapped gas in the sample based on the
expansion from the first volume to the second volume wherein the
differential between said second volume and said first volume is
indicative of the amount of gas entrapped in said material sample.
11. The method of claim 10, further comprising the step of:
(f) determining the amount of entrapped gas in the material sample either
as a percent volume of the entrapped gas within the material sample
relative to an overall volume of the material sample or an actual volume
of entrapped gas within the material sample.
12. The method of claim 11, wherein the reservoir is defined at least in
part by a barrel and a plunger, the plunger having a plunging end which
includes a wall and which is slideably engaged with the barrel, and
further comprising the steps of:
detecting an initial position of the wall prior to applying the negative
pressure to the reservoir;
detecting an adjusted position of the wall after initially applying the
negative pressure to the reservoir; and
determining the amount of entrapped gas within the material sample based
upon the adjusted position of the wall relative to an initial position of
the wall prior to applying the negative pressure to the reservoir, and
further based upon the first volume.
13. The method of claim 12, further comprising the step of detecting a zero
position of the wall prior to adding the material sample to the reservoir;
and
determining the first volume based upon the initial position relative to
the zero position.
14. The method of claim 12, wherein the plunger further has a detection end
which is separated from the plunging end with a shaft and which extends
externally of the barrel when the plunging end is engaged within the
barrel, and further comprising the step of:
detecting the position of the wall by detecting a position of the detection
end of the plunger.
15. The method of claim 10, further comprising the steps of:
(f) adding the material sample to a reservoir having a reservoir volume and
which is defined at least in part by a wall having an adjustable position
relative to the reservoir, the reservoir volume being adjustable by
adjusting the position of the wall and further being substantially equal
to the material sample volume;
(g) isolating the material sample within the reservoir with a substantially
gas tight seal;
(h) after isolating the material sample within the reservoir, applying said
negative pressure to the wall outwardly of the reservoir such that the
position of the wall is adjusted from a first position to a second
position, which first and second positions characterize the first and
second volumes, respectively; and
(i) detecting the change from the first volume to the second volume by
detecting at least one of the reservoir volume or the position of the
wall.
16. The method of claim 10, further comprising the steps of:
coupling a vacuum source to the vacuum chamber; and
applying said negative pressure to the reservoir with the vacuum source
outwardly of the vacuum chamber.
Description
FIELD OF THE INVENTION
The present invention is a test instrument and method. More specifically,
it is a device assembly and test method for determining the amount of
entrapped gas within a material sample, including a method of
manufacturing a material with a predetermined amount of entrapped gas
based upon use of the device assembly and test method.
BACKGROUND OF THE INVENTION
In many industries, there is a need to control the volume of entrapped gas
in a variety of materials so that more desirable products may be achieved.
The terms "entrapped gas" are herein intended to mean the volume of gas
which is entrapped or entrained within a substrate in a material or
sample. Furthermore, the terms "material" or "sample" are herein intended
to consist of: (1) a substrate, such as a liquid, solid, or semi-solid;
and (2) entrapped gas which is a gas that is in a gaseous state and not
dissolved within the substrate. Therefore, in simplified terms, entrapped
gas means "bubbles" of gas which are trapped within the substrate of a
material sample, which bubbles may have a volume or size ranging from
visible to microscopic or sub-microscopic.
Examples of known uses for measuring entrapped gas in products are many.
For example, in an industrial setting it is believed that the durability
of concrete may be increased by controlling the amount of entrapped gas to
a predetermined level within a concrete substrate prior to setting. In
another example, various consumer goods are also believed to rely in part
upon controlling the amount of entrapped gas in order to be sold and used
in a reliable and consistent condition. Such consumer goods may include,
without limitation: creams and ointments, such as for use in beauty care;
pastes, such as toothpaste; or various food substances, such as for
example whipped cream. In still a further example, various medical
products also require the ability to control the volume of entrapped gas
within a particular substrate in order to achieve a reliable, safe product
which provides an intended result during use. Further more specific
examples of such medical products include, without limitation:
pharmaceuticals; and medical creams, gels, and ointments.
Furthermore, the ability to control the gas content in a material is
closely related to, and in fact largely dependent upon, the ability to
measure the entrapped gas volume in the overall material. Therefore, the
ability to measure the entrapped gas volume may be of paramount importance
in the quality control of producing such materials.
In one respect, measurement of entrapped gas volume may provide indicia of
certain qualities of the overall material sample. For example, the
porosity of a sample is a direct consequence of the entrapped gas volume
within the sample and the determination of porosity of certain materials
is often desirable. In another example, for materials such as cement,
sand, gravel, and other admixtures and aggregates, it is believed that the
specific gravity and moisture content of the overall sample can be
assessed at least in part based upon the known volume of entrapped gas.
In another respect, measurement of entrapped gas volume may also provide
for the determination of specific properties of the substrate within the
sample, such as substrate volume and density. It is believed that accurate
determination of the density and volume of a substrate in a material
sample may facilitate the production for certain types of materials. For
example, density determinations can be used as a diagnostic tool for
identifying purity of the substances which form the substrate or for
indicating adulterations in preparation of known compositions. Further to
this need, measurement of entrapped gas volume may provide for a direct
determination of substrate volume, and therefore substrate density.
Substrate volume may be calculated by subtracting entrapped gas volume
from the overall sample volume. Thereafter, substrate density may
determined by multiplying the substrate volume by the substrate mass.
Conventional Devices and Methods for Measuring Entrapped Gas Volume
Various devices and methods have been previously disclosed for measuring
entrapped gas volume. For example, one known method for entrapped gas
volume includes exposing a sample to acoustic or subsonic waves. However,
it is believed that such known methods do not accurately and reliably
reflect the true amount of entrapped gas. Further more specific examples
of devices and methods of this type are variously disclosed in the
following references: U.S. Pat. No. 4,184,371; and U.S. Pat. No.
4,640,130. The disclosures of these documents are herein incorporated in
their entirety by reference thereto.
Another type of previously disclosed device which is intended to indirectly
measure substrate volume in a sample by measuring entrapped gas volume is
known as the "gas pycnometer." In general, known gas pycnometers operate
by applying a positive pressure either to a chamber which contains the
sample or to a chamber which connects to a first chamber which contains
the sample. A gas having a small molecular size, such as helium, may be
used for providing the positive pressure by entery into the pores of the
sample thereby displacing the gas, e.g. air, previously absorbed in the
pores of the sample. Consistent with the gas law stated below, the sample
volume can be determined by measuring pressure change while volumes are
kept constant or by changing the volumes and maintaining pressure within
the device. For example, two chambers may be used and one chamber injected
with gas. The pressure is measured and the gas allowed equalize between
the sample chamber and the adjoining chamber. The pressure in the combined
volume is measured and related to the sample volume. The gas law relied
upon is the following:
PV=nRT, wherein
P=pressure
V=volume
n=number of moles of gas
R=gas constant
T=absolute temperature.
Further more specific examples of gas pycnometry devices and methods such
as those just provided above are variously disclosed throughout the
following references: U.S. Pat. No. 5,133,219; U.S. Pat. No. 5,074,146;
U.S. Pat. No. 4,095,473; and U.S. Pat. No. 4,083,228. The disclosures of
these documents are herein incorporated in their entirety by reference
thereto.
SUMMARY OF THE INVENTION
The present invention is an assembly and method for measuring an amount of
entrapped gas in a material sample based upon the expansion of the
entrapped gas when the sample is exposed to a vacuum.
In one mode of the invention, an entrapped gas measurement apparatus
includes a housing with a wall which defines at least a portion of a
reservoir which is adapted to receive the material sample. The wall has an
adjustable position from a first position to a second position such that
the reservoir has an adjustable volume from a first volume to a second
volume, respectively, when the material sample is received within the
reservoir and when a predetermined force is applied to the wall outwardly
of the reservoir. The position of the wall is indicative of the volume of
the reservoir. A detector is coupled to the housing and is adapted to
measure the position of the wall. A processor is coupled to the detector
and is adapted to determine an amount of entrapped gas within the material
sample based upon a change in the position of the wall from the first
position to the second position. According to this assembly, the first
volume of the reservoir is substantially equal to a volume of the material
sample at an initial equilibrium force condition and prior to applying the
predetermined force to the wall. Furthermore, the second volume of the
reservoir is substantially equal to the volume of the material sample
under a vacuum force condition after applying the predetermined force to
the wall with a force applicator.
In a further aspect of this mode, the housing and reservoir are of a
syringe-type configuration. The reservoir is further defined by a
reservoir chamber which is relatively rigid, and the wall is moveable
relative to and encloses the reservoir chamber. The wall according to this
aspect has a zero position relative to the reservoir chamber which is
characterized by the reservoir's volume being substantially equal to zero
prior to receiving the material sample within the reservoir. When the
first position of the wall and initial equilibrium force condition are
further characterized by an equilibrium force on the wall at atmospheric
pressure, the processor determines the amount of entrapped gas at
atmospheric pressure by the equation: (d.sub.2 -d.sub.1)/(d.sub.1
-d.sub.0)* 100[P.sub.a /(P.sub.a -P.sub.v)-1], such that d.sub.o is the
zero position, d.sub.1 is the first position, d.sub.2 is the second
position, P.sub.a is atmospheric pressure, and P.sub.V is a pressure which
equals the predetermined force.
In still a more detailed variation of this syringe-type aspect, the housing
includes a barrel and a plunger. The barrel has an inner surface which
forms an inner bore with a longitudinal axis that extends between a front
end and a rearward end. The plunger has a front end and a rearward end. A
front wall is removably engaged to and is adapted to form a gas tight seal
with the front end of the barrel. The front end of the plunger is engaged
within the barrel's inner bore through the rearward end of the barrel, and
the wall is secured to the front end of the plunger and rearward wall
slideably coupled to the barrel's inner surface with a gas tight seal.
According to this configuration, the reservoir is therefore defined by the
front wall, the barrel's inner bore, and the rearward wall. The first and
second positions of the wall according to this variation are along the
longitudinal axis of the barrel's inner bore.
In another aspect of this apparatus mode, the processor may be adapted to
determine one of several parameters related to the amount of entrapped gas
in the sample. In one variation, the processor is adapted to determine the
amount of entrapped gas as a percent volume of the sample which represents
an actual volume of entrapped gas within the material sample divided by
the volume of the material sample. In another variation of this aspect,
the processor is adapted to determine the actual volume of entrapped gas
within the material sample which represents the percent volume of
entrapped gas multiplied by the volume of the material sample. In a
another variation, the processor is adapted to determine a volume of the
substrate within the sample based upon either the percent volume of the
entrapped gas or the actual volume of entrapped gas within the sample. In
yet another variation, the processor is adapted to determine a density of
the substrate based in-part upon the volume of the substrate.
In a further aspect to the entrapped gas measurement assembly mode, a force
applicator may be included in the assembly such that it is adapted to
couple to the wall and is adapted to apply a predetermined force to the
wall outwardly of the reservoir.
In one variation of this aspect, the force applicator includes a vacuum
source which is coupled to the wall and which is adapted to apply a
negative pressure to the wall. According to a further variation, a vacuum
chamber houses at least a portion of the housing that includes the wall,
and the vacuum source is coupled to the vacuum chamber and is adapted to
apply a negative pressure within the vacuum chamber. In the alternative to
the vacuum source variation, the force applicator may also be mechanically
coupled to the wall and adapted to mechanically apply the predetermined
force to the wall.
Another mode of the present invention is a method for measuring an amount
of entrapped gas in a material sample. According to this method, the
material sample is added to a reservoir which is defined at least in part
by a wall and which has a volume that is substantially equal to the sample
volume. After adding the material sample to the reservoir, a force is
applied upon the wall outwardly of the reservoir such that the reservoir
and material sample expand from a first volume to a second volume. A
parameter which is indicative of a change in reservoir volume after
applying the force upon the wall is detected and measured, which detected
and measured parameter is used to determine an amount of entrapped gas
within the material sample. The detected parameter according to this
method is at least one of the reservoir volume or a second position of the
wall relative to first position of the wall prior to applying the force to
the wall, which second position of the wall is characterized by the change
in reservoir volume.
In one aspect of this method mode of the invention, the reservoir is
defined at least in part by a barrel and a plunger, the plunger having a
plunging end which is slideably engaged within the barrel to form the
wall. The method according to this aspect further includes detecting a
position of the plunging end after applying the force to the wall. The
amount of entrapped gas within the material sample is then determined
based upon the detected position of the plunging end relative to an
initial position of the plunging end prior to applying the force onto the
wall and also relative to a zero position of the plunging end prior to
adding the material sample to the reservoir.
In a further variation of the syringe-based aspect of this method mode, a
vacuum source is coupled to the wall. Thereafter, a vacuum pressure is
applied to the wall with the vacuum source outwardly from the reservoir.
A further method mode for measuring an amount of entrapped gas within a
material sample according to the present invention includes: applying
negative pressure to the material sample, wherein the material sample
changes from a first volume to a second volume, and detecting a change in
volume from the first volume to the second volume determining an amount of
entrapped gas in the sample based on the change in volume, wherein the
amount of trapped gas is one of either a percent volume of the entrapped
gas within the material sample relative to an overall volume of the
material sample or an actual volume of entrapped gas within the material
sample.
Still a further method mode for producing a material with a predetermined
amount of entrapped gas according to the present invention includes:
forming a first material according to a first method with a first amount
of entrapped gas; applying negative pressure to a sample of the first
material, wherein the sample changes from a first volume to a second
volume; detecting the change in volume; determining the amount of
entrapped gas in the sample based on the change in volume; comparing the
determined amount of entrapped gas with a predetermined range of values;
and, when the determined amount of entrapped gas differs from the
predetermined range of values, forming a second material according to a
second method with a second amount of entrapped gas.
Thus, it is an object of the present invention to provide an assembly which
can directly and accurately determine the amount of entrapped gas in a
variety of samples.
It is a further object of the present invention to provide an apparatus
which can easily and accurately determine the density of a variety of
samples.
It is another object of the present invention to provide an gas measurement
apparatus which is easy to use and require little expertise by the
operator.
Other objects and advantages of the present invention will become more
readily apparent from the following description of preferred embodiments.
BRIEF DESCRIPTION OF THE FIGURES
FIGS. 1A thought 1D show schematic perspective views of a reservoir housing
assembly for one entrapped gas measurement apparatus during sequential
modes of use according to the present invention.
FIG. 2 shows a table of exemplary syringe sizes for use in a reservoir
housing assembly such as that shown schematically in FIG. 1.
FIG. 3 shows a perspective view of one entrapped gas measurement apparatus
for measuring entrapped gas in a material sample according to the
sequential modes of use shown schematically in FIG. 1.
FIG. 4 shows a schematic diagram of the entrapped gas measurement apparatus
shown in FIG. 3, and further shows a vacuum assembly which is coupled to
the reservoir and material sample as a force applicator for providing a
negative pressure on the material sample.
FIG. 5 shows a perspective view of another entrapped gas measurement
apparatus according to the present invention.
FIG. 6 shows an exploded perspective view of the various components of the
entrapped gas measurement apparatus shown in FIG. 5.
FIG. 7 shows a perspective view of another entrapped gas measurement
apparatus according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is an assembly which is adapted to measure entrapped
or entrained gas volume within a material sample by applying negative
pressure to the sample, measuring the resulting expansion of the sample in
response to the negative pressure, and thereafter calculating the amount
of gas in the sample. The terms "amount of gas" or variations thereof are
herein intended to mean percent (%) volume of the overall sample volume or
the actual volume of the entrapped gas within the material sample.
In general, the entrapped gas measurement apparatus of the present
invention uses a reservoir housing assembly with a reservoir which houses
a material sample to be measured. A detector monitors the reservoir's
expansion under an applied negative pressure, which expansion is a direct
concomitant to the sample's expansion under a vacuum formed within the
reservoir. A processor is adapted to determine the amount of entrapped gas
within the sample based upon the expansion of the reservoir and sample.
FIGS. 1A-D show one reservoir housing assembly (1) according to sequential
modes of use in an entrapped gas measurement assembly according to the
present invention. As shown variously throughout these FIGS. 1A-D,
reservoir housing assembly (1) is a syringe-type device which includes a
barrel (10), a plunger (20), and a loading assembly (30).
In more detail to the components shown in FIGS. 1A, barrel (10) includes an
inner surface (13) which defines an inner bore that extends between a
front end (12) and a rearward end (14). Plunger (20) includes a shaft (23)
which extends between a plunging end (22) and a detection end (24).
Plunging end (22) of plunger (20) includes a rearward wall (25) which is
adapted to slideably engage inner surface (13) of barrel (10) with a gas
tight seal when rearward wall (25) and plunging end (22) are introduced
through reaward end (14) and into the inner bore of barrel (10). Loading
assembly (30) includes a front wall (32) which is adapted to removably
engage barrel (10) such that a material sample to be measured may be
loaded within barrel (10) and then enclosed therein with a substantially
gas tight seal.
A combination assembly of the various components for reservoir housing
assembly (1) just shown and described by reference to FIG. 1A is further
shown in FIGS. 1B-D, wherein a reservoir is provided and defined by the
combination of front wall (32), inner surface (13) of barrel (10), and
rearward wall (25) of plunger (20).
The first sequential mode of use for reservoir housing assembly (1) is
shown in FIG. 1B, wherein rearward wall (25) is advanced within the inner
bore of barrel (10) such that it contacts or is positioned closely
adjacent to the front wall (32) of loading assembly (30). In this
configuration, the volume of the reservoir is substantially zero and a
baseline or "zero" position D.sub.0 for rearward wall (25) of plunger (20)
is designated by the position of the plunger's detection end (24) which
extends outside the barrel. This zero position D.sub.0 is used as a
starting reference point for measuring a change in volume of the reservoir
during subsequent modes of use according to FIGS. 1C-D as a material
sample to be measured is loaded into the reservoir and then acted upon to
expand in the reservoir under an applied negative pressure force.
FIG. 1C shows reservoir housing assembly (1) after a material sample (50)
is added to barrel (10) through loading assembly (30) and both front wall
(32) and rearward wall (25) are made to contact and completely confine
sample (50). Thus, the reservoir formed by front wall (32), inner surface
(13), and rearward wall (25) has a volume which is substantially equal to
the volume of the material sample to be measured. Further to this "sample
loading" mode of use, the new position of the plunger's detection end (24)
designates a first position D.sub.1 for rearward wall (25), and therefore
a first volume V.sub.0 when the sample is under ambient atmospheric
pressure. Thus, the movement of rearward wall (25) of plunger (20) from
the first position D.sub.0 to the second position D.sub.1 indicates a
baseline wall movement which is representative of first volume V.sub.1 for
the reservoir.
The next sequential mode of use for reservoir housing assembly (1) is shown
in FIG. 1D, wherein the portion of plunger (20) which extends outwardly
from barrel (10) is exposed to a predetermined force F which forms a
negative pressure that in turn places a force on the plunger (20)
outwardly of the reservoir. This pressure is translated to rearward wall
(25) by virtue of the rigid coupling via shaft (13) of the plunger (20),
and is further translated from rearward wall (25) and to sample (50)
contained within the reservoir. Sample (50) responds to the negative
pressure by expanding by a differential volume which is proportional to
the amount of gas entrapped within the sample. The amount or volume which
a given sample expands is determined by the expansion reaching a final
equilibrium, which may be asymptotic or absolute, which equilibrium is
believed to be defined by the pressure of the entrapped gas (which changes
during expansion) approaching the negative pressure applied to the sample.
Moreover, the force against the rearward wall (25) during sample expansion
adjusts that wall outwardly along the length of the inner surface (13) of
barrel (10), at least until rearward wall (25) reaches an equilibrium
position which is identified by a second position D.sub.2 for detection
end (24) of the plunger (20). Thus, the plunger's movement along the
distance between first position D.sub.1 and second position D.sub.2
indicates and is proportional to the change in the volume of the
reservoir, and thus of the sample, between the first volume V.sub.1 and a
second volume V.sub.2.
As summarized initially above and will be further described in more detail
below, the changing position of the plunger is directly proportional to
the volumetric change of the reservoir during the expansion of the sample
under negative pressure, and the volumetric change of the sample and
reservoir is directly proportional to the amount of entrapped gas within
the sample. Therefore, the entrapped gas measurement apparatus of the
present invention identifies the volumetric change of the reservoir by
measuring the positioning reference points (D.sub.1 an D.sub.2) of the
moveable rearward wall by use of a detector (not shown). Based upon the
detector's measurement, a processor (also not shown), such as a computer,
determines the amount of gas entrapped in the sample.
According to one operable mode for a processor which is believed to be
highly beneficial for use with the specific syringe-type embodiment just
shown and described by reference to FIGS. 1A-D, the amount of entrapped
gas within a material sample is determined as a percent (%) volume of
entrapped gas. One particularly beneficial mode for making this percent
volume determination is based upon the detected plunger position according
to the following relationships, or variations thereof:
(1) [((V.sub.E .times.P.sub.V)/V.sub.S)/1-P.sub.2 ].times.100=% air at
atmospheric pressure; and
(2) [(D.sub.2 -D.sub.1)/[(D.sub.1 -D.sub.0)*(Pa/P.sub.2)-1)].times.100=%
air at atmospheric pressure; and therefore,
(3) (D.sub.2 -D.sub.1)/(D.sub.1 -D.sub.0)*100/[P.sub.A /P.sub.A
-P.sub.v)-1]=% air at atmospheric pressure;
wherein
C=Volume constant of the reservoir;
V.sub.s =C(D.sub.1-D.sub.0)=Sample Volume at Atmospheric Pressure;
V.sub.2 =C(D.sub.2 -D.sub.0)=Sample Volume after Expansion;
V.sub.E =V.sub.2 -V.sub.S =Expansion Volume under Applied Vacuum (P.sub.v);
V.sub.E =CD.sub.2 -CD.sub.1 ;
D.sub.0 =Distance between detection end and front wall (without sample);
D.sub.1 =Distance between detection end and front wall (with sample);
D.sub.2 =Distance between detection end and front wall (before vacuum);
P.sub.A =Atmospheric pressure;
P.sub.v =Vacuum pressure; and
P.sub.2 =P.sub.A -P.sub.V.
Moreover, according to the relationship between plunger position and
applied pressure just described by equation "(3)" above, an additional
altitude correction factor may also be considered in determining the
amount of entrapped gas with the processor, wherein atmospheric pressure
P.sub.A is usually within the range of 0.75 atm to 1.10 atm. It is further
contemplated therefore that "vacuum pressure" may be any pressure which is
negative relative to a baseline which is the atmospheric pressure in the
test environment.
Further to the syringe-type barrel-and-plunger embodiment of FIGS. 1A-D,
the volume constant C provided in the analysis above for arriving at the
relationship shown by equation "(3)" represents the volume per unit length
of the barrel. In a cylindrical, non-tapered barrel, this parameter is a
direct construct of the cross-sectional area of the barrel and a constant
for the purpose of determining volume of the reservoir over ranges of
distances along the barrel (the only variable for reservoir volume is the
moveable, rearward wall). It follows that, for syringe barrels which are
not cylinders of constant diameter or cross-sectional area, the constant C
may be required as a variable in the final determining equation.
Still further to the syringe-type barrel-and-plunger embodiment just shown
and described by reference to FIGS. 1A-D, FIG. 2 additionally illustrates
measurements taken for typical reference points and other salient
characteristics of varying syringe sizes which are believed to be
particularly adapted for use according to the present invention with
samples having volumes ranging from 0 to 10 ml. The syringes represented
by the FIG. 2 table have volumes which range from 1 to 60 milliliters.
Also represented in the table of FIG. 2 are the following syringe
parameters: the zero position of the detection end for the plunger which
is indicated by a distance from the front wall of the reservoir, or
"D.sub.0 " (essentially representing the length of the plunger shaft); the
syringe volume constant which is indicated by "C" (or the cross-sectional
diameter of the barrel of the syringe); the inner diameter of the syringe
which is indicated in the table as "id"; and the maximum distance that the
opposite wall of the plunger can move to a second position after applying
a vacuum pressure to the sample, which distance is indicated by the
distance from the detecting end of the plunger to the front wall, or
"D.sub.2 ".
FIG. 3 shows one more detailed embodiment of an entrapped gas measurement
apparatus (100) which utilizes a reservoir housing assembly such as that
just shown and described by reference to FIGS. 1A-D above. Entrapped gas
measurement apparatus (100) includes a vacuum chamber (140) having a
transparent cover (143) which is adapted to couple to a negative pressure
source (not shown). The chamber contains a reservoir housing assembly
(101) that forms a reservoir which is adapted to receive and hold the
sample and is similar to the reservoir housing assembly shown in FIGS.
1A-D.
Movement of the plunger's rearward wall (125) is determined by measuring
the position of detection end (not shown) of plunger (120) with detector
(160), which is coupled to the plunger (120). In the particular variation
shown in FIG. 3, detector (160) is a linear measuring element and is
attached to the plunger at the detecting end of the plunger. The present
invention contemplates that the detector may be adapted to detect the
change in plunger position according to a variety of suitable known
mechanisms, including but not limited to optical, electrical, or
mechanical mechanisms known in the art. In addition, other various
measuring parameters may also be suitable, such as the measurement of
pressure changes in the reservoir.
In order to precisely measure pressure within the chamber of the assembly,
it is important that the chamber be made air tight. In the FIG. 3
variation, vacuum chamber (140) is sealed by two opposite caps (142,144)
each having gasket or O-ring seals, such as for example as is shown at
O-ring (145) in FIG. 3. Likewise, as shown in FIG. 6, O-ring (226)
provides a seal for barrel (210) and plunger (220) at end (222).
Preferably the O-rings are made of soft rubber for a creating an efficient
seal. In a pneumatic variation such as that shown in FIG. 3, vacuum
chamber (140) is adapted for coupling to a negative pressure source, as is
shown for example in FIG. 3 at threaded hole (146) which is adapted to
attach chamber (140) to a mated fitting from a negative pressure source.
In general, the housing which defines the reservoir may be a variety of
shapes, such as the barrel previously shown, a bulb reservoir,
rectangular, ovular tube, etc. The reservoir may be any convenient
receptacle for holding the sample as long as the reservoir is capable of
changing its volume in a manner which may be detected accurately. In
addition, the walls of the housing which form the reservoir, including a
front wall, side walls and an end wall, may be made of any suitable
material such as plastic, glass, and the like. Suitability of the material
depends, inter alia, on the design of the syringe, sample type, and
specific detector and processor embodiments chosen for detecting
volumetric change of the sample and determining volume of entrapped air,
respectively.
For example, for variations of the present invention which determine
volumetric change of the reservoir and sample based upon the position of a
moveable wall during expansion, the housing should be relatively rigid and
non-expandable in all places but for the moveable wall being monitored.
For the purpose of further illustration, where the rearward wall is made
to move laterally within a barrel in a syringe embodiment as described
above, the walls of the barrel are usually rigid and non-compliant. It is
further preferred that at least a portion of the walls be a transparent
material in order to view the sample, although the material may be opaque
as well. In addition, the construction of the various components which
comprise the reservoir chamber may also be of different materials.
In one specific example, the rearward wall is constructed of a metal such
as stainless steel or aluminum. The front wall is constructed of an
elastomeric disk such as of silicone with a rigid backing such as
aluminum, which construction is believed to provide both the elastomeric
feature for sealing the door to the housing as well as relative rigidity
against biasing the elastic disk inward into the reservoir chamber under
the applied vacuum. The barrel is constructed of glass.
However, for further illustration, the front wall and barrel may instead be
constructed of hard polymer, such as for example polycarbonate. Further to
this alternative illustrative construction, an assembly which provides a
hard polymeric front wall engaged to an adjustable door to open the
chamber for loading the sample may require the addition of a gasket or
other elastomeric sealing means to provide the desired gas tight seal in
the closed door condition during testing.
In addition, it is believed that a controlled interface between the
moveable, rearward wall of the plunger and the inner surface of the barrel
which forms the reservoir in syringe variations may be critical to
accurate determinations of entrapped gas in a tested sample within the
apparatus. In one respect, the plunger must slide within the barrel easily
and with little friction (which if excessive may be a source of error in
correlating expansion of the sample to the applied force). In another
respect, however, there must be a gas tight seal at this same interface.
Therefore, a sealing gasket, such as a soft, compliant O-ring, should be
provided at or adjacent to the rearward wall of the plunger. Suitable
material constructions and designs for such O-rings depends upon various
factor including the type of rubber comprising the O-ring, the outer
diameter at the surface upon which the O-ring sits, and the inner diameter
of the barrel.
In addition, the inner surface may be treated or modified to enhance the
movement of the rearward wall on the plunger by optimizing the friction
caused by the rearward wall sliding along the sides of the reservoir. It
is believed that surfaces which are either too smooth or too rough will
cause increased friction that may be detrimental to functional results.
Therefore, it may be desirable to create a texture on the reservoir
internal surface to a desirable roughness, such as for example through the
controlled use of abrasives. It is further believed that a surface having
a surface roughness between about 8-40.mu. inches RMS, and more preferably
between about 8-15.mu. inches, may be preferred for syringe barrels
constructed of glass or metal and for use with O-rings constructed of an
elastomer such as silicone rubber. A tensile force tester may be used to
measure the frictional component along the length of the reservoir as the
wall moves in response to force on the plunger.
Usually, the rearward wall should contact the sample such that no voids are
present between the sample and wall. However, it may be desirable in some
instances to include an intermediary material between the sample and
rearward wall of the plunger in order to provide a barrier between the
rearward wall and sample so that a variety of sample types can be tested.
The inclusion of such an intermediary material may be especially useful
when the material sample to be tested is an abrasive or gritty material
such as concrete. When an intermediary material is used, however, it is
desirable that there be no voids between the sample, intermediary material
and rearward wall.
In another respect to the plunger/sample interface, the O-ring may be
positioned along the plunger rearwardly of the rearward wall. The plunger
outer diameter is dimensioned with some tolerance gap in relation to the
inner diameter of the barrel, and this gap is generally bridged by the
O-ring. Therefore, placing the O-ring rearwardly of the rearward wall as
just described leaves the gap between the plunger and barrel forward of
the O-ring, which gap may contribute an additional, although small volume
to the overall reservoir volume. It is therefore further contemplated that
this additional volume or "dead space" may be accounted for in the overall
calculations for measuring the amount of entrapped gas in the sample, as
described in relation to various equations above. According to one
specific approach to account for this space, the dead space may be
measured by running the machine without a sample, the results of such a
"test run" yielding the amount of gas in the reservoir when at the zero or
ostensibly "no volume" state.
One example of an intermediary material of the type just described may be a
lubricant which may be added to the reservoir, such as according to the
following method: opening the reservoir at the end opposite the end wall,
applying an air-free lubricating gel over the end wall surface,
calibrating the detector to the zero position, and then filling the
reservoir with sample. The amount of lubricant can vary and is typically a
few millimeters thick or less.
Further to the variations for the entrapped gas measurement assembly just
described for the present invention, the sample expansion phenomena upon
which the invention is based requires a force applicator to provide a
force onto the moveable wall outwardly of a reservoir which is defined in
part by that wall. The present invention contemplates various mechanisms
as suitable force applicators for applying negative pressure to the
reservoir, e.g. pneumatic source as in a vacuum, mechanical force as in a
device for pulling or pushing the moveable wall down the length of the
housing in a direction away from the sample (thereby creating a vacuum on
the sample), or other sources known in the art.
FIG. 4 shows a slightly different side view for entrapped gas measurement
apparatus (100) shown in FIG. 3, and also provides a vacuum pump (170) as
a force applicator which applies negative pressure to the sample to cause
expansion of the sample. Vacuum pump (170) is pneumatically coupled to
chamber (140) through attachment (172). A vacuum regulator (174) controls
the amount of negative pressure applied to chamber (140) and vacuum gauge
(176) reads the pressure within the chamber.
The amount of negative pressure applied depends, inter alia, on the type
and amount of sample present and the volume of the reservoir. Typically
the amount of negative pressure applied to the chamber is from about 5
inches to 30 inches Hg, more typically from about 10 inches to 27 inches
Hg and preferably from 15 inches to 25 inches Hg. Preferably the vacuum
pump is capable of producing 25 inches Hg when connected to a 110 V AC
power source. The vacuum is preferably applied at a rate which is
generally slow and consistent with the rate of sample expansion in order
to avoid caving in of the sample or cavitation which may occur if vacuum
is applied at a rate faster than sample expansion. The rate of change in
applying the vacuum is generally from about 10 seconds to 300 seconds,
more often from about 20 seconds to 120 seconds, and preferably from 30
seconds to 60 seconds, and usually about 30 seconds for most types of
samples.
The present invention also contemplates various detectors as being suitable
for use in monitoring and detecting the position of a moveable wall as a
determinant of the expanding volume of a reservoir and material sample.
One particular detector which is believed to be particularly beneficial
for use in the present invention is shown in FIG. 5.
FIG. 5 shows entrapped gas measurement assembly (200) to include a
reservoir housing assembly (201) to include a barrel (210), plunger (220),
and loading assembly (230) and is similar in structure and operation to
the syringe-type reservoir housing assemblies shown previously in FIGS.
1A-B and FIGS. 3 and 4. However, the variation shown in FIG. 5 provides a
rail (266) with which detection end (224) of plunger (220) is slideably
engaged and along which a detector assembly (260) is adapted to detect the
position and travel of the plunger.
In more detail to detector assembly (260) shown in FIG. 5, rail assembly
(265) includes rail (266) which extends between a front support base (267)
and a rearward support base (268). Detection end (224) of plunger (220) is
secured to a rail coupler (269) which is slideably engaged with rail
(266). Rail (266) has graduations (266') in predetermined, marked
increments along its length. A linear measuring device marks the movement
of rail coupler (269) along rail (266) according to graduations (266'),
and is integral to the rail coupler (269) in the FIG. 5 variation and
therefore not shown. Other position detectors than the specific "rail
graduation monitoring" mode just described may also be suitable. In one
example not shown, the detector may include an optical sensor optically
coupled to indicia along the rail in order to indicate relative position
of the plunger. In another example also not shown, the detector includes
an electronic sensor coupled to the rail in a manner which indicates the
relative position of the sensor and therefore the plunger. Further to this
particular example, such electronic coupling may result in the desired
indicia of relative sensor position via monitored electronic parameters of
a circuit which couples the sensor to the rail, such as for example by a
varied capacitance, inductance, or resistance monitored by the sensor as
the plunger is moved.
The linear measuring device is coupled with processor (280) (shown in FIG.
5 schematically and in shadow) by use of a data cable (282) which
transfers the detected position of the plunger to processor (280) via
connector (281). Preferably, processor (280) includes a microprocessor or
CPU which is adapted to receive detected signals through the connector
such as through an RS232 coupling according to one of ordinary skill. The
CPU according to such a variation would be further adapted to process the
detected positioning signal according to the relationships described above
between position, pressure, and entrapped gas volume, such as through
software provided within the CPU or readable memory coupled to the CPU.
More specific details of the components which make up entrapped gas
measurement apparatus (200), including various attachment mechanisms, are
shown in FIG. 7, and in more specific detail in exploded view in FIG. 6
and are described as follows.
Reservoir housing assembly (201) includes a barrel (210) with an inner
surface (213) which defines an inner bore that extends between a front end
(212) and a rearward end (214). The inner bore of barrel (210) in the
region of its front end (212) is engaged to and registered with opening
(233) of loading assembly (230). Loading assembly further includes a door
(231) which is adapted to removably engage and interchangeably open or
close opening (233) such that a sample (not shown), intermediary
materials, etc., may be added to the barrel and then enclosed therein.
Barrel (210) is adapted to secured to loading assembly (230) on front
support base (267) by locking ring (235) and associated screws and inserts
such that the aperture (236) in locking ring (235) aligns with the front
end (212) of the barrel and loading assembly opening (233). The door (231)
is sealed against base (267) with a gasket, and the loading assembly
elements are further secured by additional pins. It is further
contemplated that the sealing gasket for door (231) may be constructed of
a specifically chosen material, which may be different to the material
comprising the remaining mass of the door. This is due to the fact that
this portion may be in direct contact with the sample during testing, and
the particular material may depend upon the type of material sample used.
Front end (222) of plunger (220) which forms the rearward wall of the
resulting reservoir is adapted to engage the inner bore of barrel (210) at
the opposite extremity at which the barrel is secured to the loading
assembly. Detection end (224) of plunger (220) extends externally of the
barrel in order to engage rail coupler (269).
Further to the detailed components of rail assembly (265) as shown
variously in FIGS. 5 and 6, one end of rail (266) is coupled to rearward
support base (268) by base cap (268') with associated screws. The rail's
other end is inserted into front support base (267) at aperture (267').
The previously described embodiments above generally share use of a
relatively rigid reservoir but for a moveable wall which is monitored
during sample expansion. However, as previously described a wide variety
of sample reservoirs, force applicators, and detectors which may be used
in combination and still fall within the scope of the present invention,
so long as a negative pressure is applied to a material sample and the
material sample's expansion under that vacuum is detected and used to
determine the amount of entrapped gas within the sample. FIG. 7 shows a
further entrapped gas measuring apparatus embodiment which exemplifies
such a broad scope, wherein the entire reservoir is expandable under
applied negative pressure.
More particularly, FIG. 7 shows a reservoir housing assembly (301) that
includes an elastic container, which is shown in a particular variation in
FIG. 7 to be a bulb (310). Bulb (310) is submersed in a non-compressible
liquid (320) such as water. A fluid chamber (340) contains the liquid to a
base level D.sub.0, which indicates the bulb's volume being substantially
zero prior to inserting a material sample within the bulb. Preferably,
bulb (310) is submersed a sufficient depth under the liquid level such
that a positive pressure actually forces the bulb to the substantially
zero volume state. After the bulb is filled with a material sample, such
as by injecting the sample within the bulb, an initial liquid level is
measured as D.sub.1, which is analogous to the first position of the
plunger in the previous syringe-type embodiments. Negative pressure is
then applied to the liquid from a pressure source (not shown) and imparted
onto the sample. Expansion of the sample upon exposure to the pressure
causes the bulb to expand thereupon changing the level of the fluid to
D.sub.2. The change in fluid level is measured as representative of sample
expansion and the amount of gas entrapped in the sample.
The amount of entrapped gas may be calculated in large part by using the
relationships between changing volume and pressures described by reference
to the previous embodiments above or variations thereto. One variation
which may better accommodate the present embodiment of FIG. 7 may include
a pressure offset for an initial equilibrium pressure that is not
atmospheric pressure, but is instead dependent upon the bulb's depth
within the fluid bath. Alternatively, the zero volume point may be set
after an initial application of an offset vacuum force which itself
accommodates this pressure offset due to the bulb's depth.
In addition, according to the compliant reservoir variation of FIG. 7, the
expansion of the bulb under pressure will be partially related to the
mechanic stress-strain properties which are characteristic of the material
used for the bulb. Therefore, the formulas used to extrapolate the amount
of gas present in the sample may require compensation for this component
of the bulb's expansion. Further to this aspect, it is preferable that the
material and pressures are chosen for testing such that the bulb expands
only along a substantially linear portion of the bulb material's
characteristic stress-strain curve in order to best accommodate this
offset to the expansion/entrapped air relationships.
Entrapped gas measurement assemblies according to the embodiments
previously shown and described for the mechanical features of the
invention preferably interface with automation instrumentation. The
entrapped gas measurement assembly is used in conjunction with a
conventional microprocessor, such as a computer to calculate the amount of
gas present in the sample. Instrumentation can also be employed to record
and store data, perform statistical analysis of replicate measurements,
maintain temperature, control negative pressure in the chamber, correct
for variations in barometric pressure relative to standard atmospheric
pressure, etc. A printer can also be incorporated into the system to
provide a hard copy of the results. With the assistance of the
instrumentation, the gas measurement system is easy to operate, requiring
little expertise by the user.
In use of the syringe-plunger configurations of the invention previously
described above, the operator adds the sample to the reservoir. The
reservoir and accompanying syringe-plunger components may be positioned in
a horizontal position in the vacuum chamber, although it is believed that
frictional sources of error are best minimized by placing the reservoir
assembly vertically, especially where the sample may flow out of the
reservoir. Where the device includes a removeably engageable front end
wall, the end wall may be removed from the reservoir to add the sample and
the end wall inserted into the reservoir to firmly contact the sample.
Alternatively, the sample is added through a loading assembly at the front
end of the reservoir to contact the end wall and the end wall remains in
place, such as the door in the loading assemblies previously shown and
described above. Moreover, the plunger and barrel of the syringe-type
reservoir may be removed and loaded and then replaced back into the
chamber. Which ever method is used to add the sample to the reservoir, the
procedure should disallow excessive handling of the sample in order to
avoid de-aeration of the sample.
The present invention is adapted for use with a variety of materials as
material samples for testing, and in particular is amenable to materials
constructed of substrates which allow for the expansion of the gas
entrapped by the substrate when a sample of the material is exposed to an
applied negative pressure. More specific examples of materials
contemplated for use with the present invention include: finely divided
solids, e.g. powders; semi-solids, e.g. gels; and liquids, e.g. ointments.
The amount of sample also may vary depending on the type of sample used
and reservoir size, typically from about 0.5 to 100 ml, more typically
from about 1 to 10 ml and preferably from 2 to 5 ml. It is further
believed that the invention may also be useful in determining the amount
of entrapped gas within certain material samples of open cell solids, or
elastic closed cell solids, e.g. closed cell foam elastomers.
Some such test materials as just described may include substrates which
yield under applied vacuum and therefore contribute to the overall
expansion of a material sample during evaluation according to the present
invention. It is believed that the present invention may still be amenable
to use with such materials, so long as the yield of the respective
substrate is predictable, such as for example calculable for a measured
weight of the sample. In such a circumstance, the calculations used to
determine the amount of entrapped air based upon measured sample
expansion, as provided above, may include still a further factor which
accounts for such substrate expansion to thus remove what may otherwise be
error in the overall entrapped gas determination. Moreover, material
samples having a known viscosity in a particular reservoir chamber may
also present some amount of fluid shear along the boundaries the chamber
walls which may also contribute to the overall material expansion under
applied vacuum in combination with the expansion of the entrapped air. It
is also further contemplated that the predictability and amount of such
shear forces may be calculable and accounted for in the operable
calculations in order to accurately make the overall determination of the
amount of entrapped gas in the sample according to the present invention.
It is further contemplated that, as the sample expands during testing with
an apparatus according to the present invention, the temperature of the
inside of the reservoir may decrease. However, with small sample sizes,
any temperature fluctuation which occurs is generally negligible. With
large sample sizes, however, the temperature may decrease to a greater
extent and temperature may be monitored with a sensor and compensated for
in calculating sample volume. For example, such compensation may be made
by use of known relationships according to the gas law: PV=nRT where P is
pressure, V is volume, n is moles, R is a constant and T is temperature.
After the volume of the sample has arrived at relative equilibrium and
ceases to substantially expand further, the vacuum pressure is stabilized
and the volume of the reservoir is detected. This equilibrium point may be
identified visually with manual control to stabilize the pressure and take
a measurement with the detector and processor, or more automated feedback
control mechanisms may be employed. For example, the detector and/or
processor may be preset to identify a predetermined value which represents
equilibrium, such as a predetermined slope or time rate of change of the
wall movement. Upon identifying that such a predetermined set-point is
reached, the pressure may then be automatically adjusted and measurement
taken from the detector for the purpose of determining the amount of
entrapped gas. Regardless of the specific mechanism used for determining
the equilibrium point, the amount of volumetric change is related to the
amount of entrapped gas in the sample, conveniently by a computer or other
automated means.
The present invention further contemplates particular methods for using the
entrapped gas measuring apparatus embodiments previously described above
by reference to the Figures, which methods of use are believed to be
particularly beneficial in the production of materials with known amounts
of entrapped gas.
One exemplary method for using the apparatus of the present invention in
the production of a material with known entrapped gas volume is provided
as follows. A first material is made according to a first method, such
that a first amount of entrapped gas is present in the material. The
amount of entrapped gas in this first material is then measured according
to at least one of the assemblies and methods of use previously described
above by reference to the embodiments in the Figures. The measured amount
of entrapped gas in the material sample is then compared with detecting a
predetermined range for entrapped gas volume or amount. If the measured
amount is within the predetermined range, then the first sample is
acceptable and is made with a predetermined amount of entrapped gas.
Thus a "predetermined amount of entrapped gas" is herein intended to mean
an amount which is either a specific amount, such as actual volume or
percent volume of the sample, or within a particular predetermined range.
Further to this intended meaning, the "predetermined amount of entrapped
gas" may be either substantially zero (it is believed that most all
manufactured substances have some residual amounts of entrapped gas,
although in many circumstances negligibly small), or may be a non-zero
amount, such as according to methods intended to provide a desired amount
of entrapped gas in a material or according to other methods intended to
remove all gas in a material but allowing for some measurable tolerance
which reflects a range of values bounded at zero.
If the determined amount of entrapped gas in the first material sample is
not within the predetermined range, then a second material is made
according to a second method, wherein the second method is intended to
affect the resulting amount of entrapped gas in a desired direction from
the first method and material (either increasing or decreasing the
resultant amount as required). For example, the first method may employ a
particular operating parameter which affects the amount of entrapped gas
in the material produced, and the second method may be a modification of
the first method wherein the operating parameter is adjusted based upon
the determined entrapped gas amount in the first sample produced by the
first method. The second material is then tested with the inventive
apparatus and method and compared with the predetermined range. Such
iterations may be repeated until a resulting material finally meets the
required entrapped gas volume.
Further to this method of producing a material sample of known amount of
entrapped gas, other parameters than actual expanded volume may be
compared against predetermined ranges for such parameters. For example,
the position of a moveable wall defining the reservoir, as previously
described above, may be such a suitable parameter. In addition, the method
just described is believed to be useful with a variety of specific methods
for constructing various materials as would be apparent to one of ordinary
skill.
EXAMPLE
For the purpose of further illustration, the following is an example of
entrapped gas volume determinations for certain material samples, in
particular commercially available whipping cream, using an entrapped gas
measurement apparatus and method which exemplifies the various particular
embodiments described above. For all of the examples provided below, a
control method is used to determine the density of the material samples,
such as for example by use of a specific gravity bottle or pycnometer,
such as Model 1620-25 which is commercially available from Corning, Inc. A
control measurement for the amount of entrapped air of a sample is made by
measuring and comparing density before and after introduction of air into
the sample. The amount of entrapped gas in the sample is also determined
by use of an entrapped gas measurement assembly according to the present
invention, and is compared against the control methods.
More specifically, a 15 ml syringe is used with a plunger at a position
(D.sub.0) designated as zero prior to sample addition. The plunger is
removed and a sample consisting of 3 ml Clover Stornetta Heavy Whipping
Cream (from Clover Stornetta Corporation, located Sonoma, Calif., Lot #
2045) is placed inside of the syringe. The whipped cream is pre-beaten in
order to entrap gas in the standard method and until the whipped product
is at its stiff peak stage. The plunger is replaced inside of the syringe
to contact with the Cream. The position of the plunger (D1) is detected by
a linear position detector and the pressure of the syringe (Pa) at
atmospheric pressure is measured in inches Hg. The data are recorded by a
computer. Next, an attached vacuum pump (Model SOAV105NA from GAST
Manufacturing Corporation, located in Benton Harbor, Mich.) is activated
to create a vacuum pressure inside of the syringe. After about 1 minute,
the sample has expanded to substantial equilibrium and the vacuum is
stabilized. The position of the plunger (D2) and the pressure inside of
the syringe (P2) are again detected. The amount of change is related to
the amount of entrapped gas in the sample. From this data, density of the
sample is determined. The results of two tests according to the test
method just described are as follows:
______________________________________
Test 1
D (in) = 0
D1 (in) = 0.6835
D2 (in) = 1.9642
Pa in Hg = 30
P2 vac. in Hg = 25
______________________________________
% Entrapped Gas Result (Gas Volume * 100/Sample Volume):
Vacuum/Expansion method =
37.47
Densitometer/Control method =
36.87
______________________________________
Test 2
D (in) = 0
D1 (in) = 0.5975
D2 (in) = 1.313
Pa in Hg = 30
P2 vac. in Hg = 22
______________________________________
% Entrapped Gas Result (Gas Volume * 100/Sample Volume):
Vacuum/Expansion Method =
43.55%
Densitometer/Control Method =
42.44%
______________________________________
The present invention has been described above in varied detail by
reference to the particular embodiments and Figures. However, it is to be
further understood that other modifications or substitutions may be made
to the devices and methods described based upon this disclosure without
departing from the broad scope of the invention.
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